822 FXUS64 KBMX 211210 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 610 AM CST Fri Dec 21 2018 .UPDATE... For 12Z Aviation. && .SHORT TERM... Today through Saturday night. Regional radar currently shows scattered to numerous rain showers across much of the state. Rain showers will decrease from west to east today as the upper low progresses northeast. The tightening pressure gradient on the back side of the surface low will allow for surface wind gusts 20-30mph throughout the day. Overall, temperatures will be cooler due to a greater influence of cold air advection. River fog cannot be ruled out tonight as clouds clear out and winds become light. Forecast soundings indicate the airmass will become very dry just above the surface. Higher boundary layer winds will also keep fog confined to mainly water bodies. Saturday looks to be dry with high temperatures in the middle to upper 50's. The next chance for a few showers will be early Sunday morning as a weak surface low moves across northern Mississippi. Weak warm advection, 60% RH values and PWAT values 0.75-0.8 could support a chance of a few showers in our northwest counties. Surface temperatures Saturday night will be warm enough across the northwest counties to keep precipitation in liquid form. 07 .LONG TERM... Sunday through Tuesday. Much of the country will be under an upper-level split-flow regime with no particulary amplified troughs/ridges heading into Sunday and early next week. This setup will act as a broad thoroughfare for transient shortwaves to traverse from west to east across the eastern two-thirds of the US. The first and more prominent shortwave is expected to approach our region in the Sunday timeframe where downstream airmass modification supports enough moisture return to produce scattered light rain showers across central Alabama. Most of this light rain activity should stay focused along a weak low pressure area and associated frontal boundary and should be near the I-20 corridor ~12 PM Sunday. A southeastward progression is expected with diminishing coverage/intensity of rain showers heading into the overnight hours. Cooler & drier air advects into the region as a stable continental airmass/high pressure area settles across the southeastern CONUS into Christmas Day. Another perturbation is expected to pass by to our north on the holiday and bring the possibility of an isolated shower to the area, but moisture will remain limited due to the antecedent high pressure system. Highs in the 50s/60s will be the overall theme in the afternoon though temperatures will be a little cooler in areas receiving cloud cover & light rain Sunday/Monday. Wednesday through Friday. There are continued indications of a more potent & amplified disturbance to enter the Desert Southwest around Wednesday. Downstream conditions will undergo broad moisture/temperature increases as mid/upper-level ridging develops across the Southern Gulf Coast states. This sets the stage for the busy upper- tropospheric circulation to tap into northwestern Gulf moisture as the trough ejects from the southern Rockies into the Plains by Thursday. With low predictability within the split-flow regime this far out it's difficult to forecast the trajectory of the wave and where associated cyclogenesis/surface features develop. So, the general theme of the long-term forecast is best advertised as a period of wet & unsettled weather to move into our area, particularly in the Thursday/Friday timeframe. A slight chance of thunderstorms has been introduced on Thursday given the overall evolving synoptic pattern indicating the potential for instability to become available as well. For now the primary threat will be periods of moderate/heavy rainfall to affect the area and further support a continuance of the busy hemispheric pattern & above average precipitation for central Alabama. 40/Sizemore && .AVIATION... 12Z TAF Discussion. A highly amplified upper trof axis will pass thru Alabama this morning. The trof will produce widespread light rain thru 18z, with the rain ending from west to east during the afternoon. A tight pressure gradient on the back side of the upper trof will produce northwest winds 10-15 kts with gust up to 25 kts. The winds will slowly weaken after 00z, becoming near 5 kts by 06z. Despite the rain and cold air advection, cig heights have been rising and many locations are now between 1000 and 1500 feet agl. Cigs heights will likely stay steady thru 18z, then slowly rise. MVFR cigs will likely prevail until the cigs become scattered later in the period. Clouds will clear across west Alabama this evening with the clearing line spreading eastward overnight. 58/rose && .FIRE WEATHER... Cloudy skies and light rain will prevail today before beginning to taper off towards the northeast into the overnight hours. A brief period of clearer skies and drier weather is expected on Saturday before scattered light rain showers develop on Sunday. With expected rainfall and relative humidity values remaining above critical values, there are no fire weather concerns at this time. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 46 30 52 35 53 / 80 20 0 10 40 Anniston 47 31 53 36 56 / 80 20 10 0 40 Birmingham 45 32 55 40 55 / 70 10 0 10 40 Tuscaloosa 45 32 58 42 59 / 50 0 0 10 40 Calera 45 31 55 39 57 / 70 10 0 10 30 Auburn 47 33 54 38 59 / 80 10 0 0 20 Montgomery 47 33 57 38 64 / 60 0 0 0 20 Troy 47 34 57 37 65 / 60 0 0 0 10 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$